The present invention relates to a rotating dynamoelectric machine such as a variable-reluctance motor, comprising a stator magnetic circuit provided with windings in and a rotor magnetic circuit.
The stator magnetic circuit can be either inside the rotor magnetic circuit as in FR-A-2329097 which describes a wheel-motor in which the electrical phases are distributed angularly about the axis of rotation Z, or outside as in FR-A-2203212 in which the single-phase structures are juxtaposed along the axis of rotation Z.
If the magnetic circuits are formed by stacks of thin metal sheets along the axis Z, cutting-out of these sheets calls in both cases for substantial tool equipment and results in losses of material. Furthermore, in the case of FR-A-2203212, the flux has to pass from one sheet to another through parasitic reluctances.
DE-A-2302323 also describes juxtaposed structures. The stator magnetic circuit and the rotor magnetic circuit are each formed by an assembly of eight independent angular sectors each constituted by metal sheets, the plane of which passes substantially through the axis of the motor. The stator sectors have a U shape and straddle a phase winding and the rotor sectors are rectangular. There is little loss of material, there is no longer any joint reluctance and the flux path is as short as possible.
However, in order to have sufficient core cross-sections, it is found necessary to have one stack of metal sheets per sector. It is also preferable to have an airgap area of small length in order to reduce its perimeter along which are formed fluxes having low-efficiency fringes. Closure by overlapping of an airgap is accordingly carried out sheet by sheet and abruptly in the case of each sheet instead of simultaneously in the case of all the sheets and progressively in the case of each sheet. This results in considerable core losses since the flux has to be established abruptly in the case of each sheet and has to pass from one sheet to the adjacent sheet in order to spread out.
DE-A-2727450 describes a synchronous or stepping motor composed of a plurality of single-phase structures juxtaposed coaxially with an axis of rotation. Each structure comprises in accordance with FIGS. 6 and 7:
a stator magnetic circuit constituted by an assembly of stator angular sectors arranged in a circle about the axis of rotation, each sector as seen in a direction tangential to the axis f rotation being given a U-shaped profile having two arms, the entire series of arms of the sectors being provided at the free ends of at least one set of arms with a row of stator teeth;
a stator winding coaxial with the axis of rotation and housed within U-shaped sectional members of the stator magnetic circuit;
a rotor magnetic circuit in which provision is made for two rows of rotor teeth each located opposite to one row of stator teeth so as to constitute two annular rows of airgaps.
If the permanent magnets 19 and 20 were suppressed, this would result in variable-reluctance operation.
In accordance with the above-mentioned patent document, the magnetic circuits are of soft magnetic material in either sintered or massive form with joints. In both cases, substantial core losses result. Furthermore, sintered parts involve high tooling costs and a limitation of the size of motors.
In order to be able to operate at high speeds and therefore at high switching frequencies, it is desirable to make use of metal sheets of small thickness having oriented grains. It is difficult, however, to form a stack of sheets which have a thickness of 0.1 mm, for example, and which lack rigidity. Assembly rivets have to be insulated, bring about a loss of core cross-section, and do not make it possible to have a stack of sheets which are tightly clamped together over their entire surface. Moreover, the preferred orientation of the grains cannot correspond at all points to the passing of the flux which changes direction. Finally, assembly of these metal sheets is costly and liable to impair their insulating film.
There is known in this connection, according to U.S. Pat. No. 4,223,255, a C-shaped magnetic circuit core constituted by an assembly of strips of sheet metal having high permeability and bent twice. These cores are employed in the stator of a permanent-magnet stepping motor which does not operate by variation of reluctance. Furthermore, the ends of these cores are located in the same plane at rights angles to the axis of rotation and opposite to permanent magnets.
This patent document is therefore no adapted to use in a variable reluctance motor since these motors require teeth within cylindrical airgaps between a stator and a rotor. Moreover, this document does not give any indications in regard to the method of assembly of said strips of sheet metal.
The object of the present invention is to overcome the drawbacks mentioned in the foregoing.
The variable-reluctance dynamoelectric machine which forms the subject of the invention comprises a plurality of structures juxtaposed coaxially with an axis of rotation Z, each structure being constituted by a stator magnetic circuit and a rotor magnetic circuit which are concentric with one another, the stator magnetic circuit being constituted by an assembly of stator angular sectors arranged in a circle about the axis of rotation Z and having, as seen in a direction tangential to the axis of rotation Z, a U-shaped profile having two arms, the entire series of arms of the stator sectors being provided at the free ends of each set of arms with a row of stator teeth located opposite to another row of teeth forming part of the rotor magnetic circuit so as to constitute two rows of airgaps of annular shape, a stator winding 15 of toroidal shape which is concentric with the axis of rotation Z being housed within the U-shaped profiles.
The rotor magnetic circuit can also be constituted by an assembly of a plurality of rotor angular sectors arranged in a circle about the axis of rotation.
An elementary magnetic loop of a structure is constituted by two airgaps of different rows, having substantially the same angular setting and coupled by the stator and rotor sectors, the stator winding being adapted to pass through said loop.
The angular positions of closure of the airgaps of each structure are angularly displaced with respect to those of the other structures.
In the case of a variable-reluctance motor, the stator windings of the different structures are connected sequentially under the control of switching means according to the position of the rotor.
The ampere-turns in the windings produce a flux having a direction transverse to the local direction of motion.
In accordance with the invention, the stator angular sectors and preferably also the rotor sectors are arches each constituted by a stack of strips of magnetic sheet which are bent to different radii about bending axes having a direction which is transverse to the axis of rotation. Furthermore, the stator teeth and preferably the rotor teeth having cylindrical airgap surfaces are constituted by a portion of the sheets. Finally, in said teeth, the teeth extend in planes substantially perpendicular to the axis of rotation.
Preferably, the strips of sheet metal are obtained from a thin magnetic sheet having oriented grains, the orientation of which is transverse to the direction of the bending axes so as to ensure that the orientation of the grains corresponds at all points to the direction of passage of the flux. Moreover, the shortest bending radii are greater than six.
Finally, the invention contemplates the case in which the rotor magnetic circuit accommodates a source of rotor magnetomotive force constituted either by a rotor winding of toroidal shape housed within a channel or by permanent magnets each interposed in a cut-out portion of a rotor arch.